Bay's tidal pools could be ancient Pfiesteria habitat Pollution may have triggered migration to deeper waters

October 10, 1997|By Douglas M. Birch | Douglas M. Birch,SUN STAFF

ST. LEONARD -- Scientists at a small research laboratory have tracked Pfiesteria to a tidal marsh near here, the type of habitat where, they suspect, the microbe may have puttered along placidly for millions of years before rising pollution helped it thrive in deeper waters.

Over the past two summers, scientists at the Academy of Natural Sciences' Estuarine Research Center have netted fish from a marsh on the shore of the Patuxent River and placed the fish in tanks in a basement lab. Twice they have arrived in the morning to find the fish stunned, pockmarked by sores or floating dead in the cloudy water.

Each time, the culprit was tentatively identified as Pfiesteria piscicida, a single-celled organism that ambushes its prey with powerful toxins.

That microorganism has been blamed in recent months for injuring and killing fish in North Carolina, Virginia and Maryland's lower Eastern Shore, and for causing memory loss and other ailments among some people who work on the water.

Denise L. Breitburg, a fish ecologist and assistant curator of the Calvert County center, pointed out that Pfiesteria-like organisms seem to prefer shallow, still waters rich in nutrients and jammed with fish. That describes perfectly some of the puddles left behind when the tide pulls out of a marsh.

"The ecology of the organism is such that it seems like these inter-tidal marshes are the ideal habitat for it," Breitburg said.

No Pfiesteria-related fish kills or suspicious illnesses have been reported in the wild along the Patuxent River. But concern remains. The Department of Natural Resources this week sent field biologists to the Patuxent to take water and sediment samples, as well as collect and examine fish for signs of Pfiesteria-related lesions.

John R. Griffin, state secretary of natural resources, said Tuesday that of 914 fish his staff pulled from the Patuxent in mid-September, "Six of them seemed to have something like a Pfiesteria lesion."

He said he considers the percentage of sick fish "negligible" but that the state will continue to monitor the Patuxent until the weather turns cold. "Either it's in a toxic form, but at so low a level that it's not creating a problem with humans, or it's in its nontoxic form," he said.

No symptoms

No one at the Estuarine Research Center has developed symptoms, Breitburg said.

She said the organism might have typically lived in shallow, still and nutrient-rich tidal ponds along the Chesapeake Bay. As pollution raised nutrient levels and caused other changes in the bay's tributaries, conditions could have ripened for explosive blooms of the organism.

"Through migration or rainfall, they may be flushed out into the river," Breitburg said. "And they may thrive in the river if nutrients are high and there are really high fish densities. That could be a likely scenario.

"This is just a hypothesis, but I think this is a real intriguing possibility."

Breitburg and her colleagues hope to use the marsh as a natural laboratory for the study of Pfiesteria's life cycle in the wild.

They tracked the microbe to the marsh last month, when Jeff Smallwood, a 25-year-old staff scientist with the research center, pulled on hip waders and stomped through the pungent muck of a creek through the marsh, which is about a mile west of the research center.

Hunting amid the marsh grass at low tide, he found a puddle of brackish water that seemed different from the rest: It contained a few tiny fish and was covered with a thin milk-white froth.

"The water just looked funny enough there that I decided to take some water samples," Smallwood said. He sent the samples to JoAnn Burkholder, one of the scientists who discovered and named the microbe. Her lab at North Carolina State University confirmed that Pfiesteria was probably in the water.

"Jeff was incredibly observant," said Richard V. Lacouture, a phytoplankton specialist at the research center who has studied Pfiesteria for several years.

He pointed out that the organism, which has 24 life stages, is difficult to identify except when it briefly assumes one of several fish-killing forms. Burkholder's lab couldn't find Pfiesteria in a water sample Smallwood took from another puddle, which contained no fish, or in other samples that Department of Natural Resources workers had taken from the marsh.

Breitburg's first encounter with the microbe, a member of a class of marine organisms known as dinoflagellates, came three years ago, when the Estuarine Research Center was in Benedict, on the western shore of the Patuxent River in Charles County.

Breitburg scooped live fish off the end of a dock of an old oyster cannery in late 1993, planning to use them for an experiment. She wanted to determine whether she could trick fish into spawning by mimicking summer conditions in the lab by artificially raising the water temperature and lengthening the period of light.